In certain electrostatographic imaging and recording processes such as electrophotographic copying processes, an electrostatic latent image formed on a photoconductive surface is developed with a thermoplastic toner powder which is thereafter fused to a substrate. The fusing step commonly involves directly contacting the substrate, such as a sheet of paper on which toner powder is distributed in an imagewise pattern, with a heated fusing member such as a fuser roll. In most instances, as the powder image is tackified by heat, part of the image carried by the sheet sticks to the surface of the roll so that as the next sheet is advanced, the tackified image partially removed from the first sheet partly transfers to the next sheet and at the same time part of the tackified image from the next sheet adheres to the heated roll. Any toner remaining adhered to the heated surface can cause a false offset image to appear on the next sheet that contacts the fusing roll and can also degrade the fusing performance of the fusing surface.
To prevent toner offset, many expedients have been tried such as providing the fusing roll with an adhesive surface such as a thin coating of an elastomer, e.g., a fluoroelastomer, or a silicone polymer of low surface energy. Also polymeric release oils, e.g., polydiorganosiloxane release oils such as polydimethylsiloxane release oils have been applied to the fuser roll surface. With such materials, however, problems can occur. One problem is that the fluoro-elastomers and silicone polymers are difficult to wet with polymeric release oils and the application of excessive amounts of such oils to the surfaces of fuser rolls in order to achieve sufficient surface wetting can cause oil stains on the paper to which toner is being fused.
U.S. Pat. Nos. 4,264,181 and 4,272,179 describe fuser rolls having surfaces comprising fluoroelastomers and metal-containing fillers that provide sites that react with functionalized polymeric release agents such as mercapto-functional polydiorganosiloxane release agents to provide a surface adhesive to toner materials and reduce toner offset. Unfortunately, as such fuser rolls wear, fresh active sites that are exposed react not only with the functionalized polymeric release agents but also react with various components of the toner materials and the paper substrate. Such reaction builds up debris on the surface of the fuser roll which results in permanent damage to such surface. This greatly reduces the life of the fuser roll. Additionally, the metal-containing filler particles are physically torn from the fuser surface during use which also reduces the life of the fuser roll. Use of mercapto-functional polydiorgano-siloxane release agents is also undesirable because of concerns relating to toxicity and unpleasant odors.
U.S. Pat. Nos. 4,029,827, 4,101,686 and 4,185,140 also describe the use of functionalized polymeric release agents with heated fusing members.
It is toward the objective of providing an improved method of fusing heat-softenable toner images--using a particular combination of release oil and fusing member surface--that the present invention is directed.